In recent years, panels used for automobiles and the like are required to be reduced in weight. An example of a method for weight reduction is to reduce sheet thickness. A reduction in sheet thickness, however, causes a problem in that rigidity is lowered. Hence, to ensure rigidity without increasing sheet thickness, forming protrusions and recesses in a panel is proposed. The protrusions and recesses are required to be formed with a depth as small as possible in order to suppress interference with other components.
JP 5218633B discloses a panel having a plurality of protrusions and a plurality of recesses. Each protrusion has a flat top face. Each recess has a flat bottom face. The protrusions and the recesses are alternately arranged in rows and columns.
JP 2012-148290A discloses a sheet material having protrusions and recesses. In this sheet material, many imaginary squares are combined vertically and horizontally to form a sheet surface, and the sheet surface has a protrusion-and-recess pattern. A basic configuration, where first and second regions are formed in the imaginary square, and more than one of various basic configurations derived from the basic configuration are butted together at their peripheral edges such that the first regions are butted together and the second regions are butted together; thus, an entire configuration of the sheet surface is obtained. The sheet material is configured in a manner that the protrusion-and-recess pattern is formed over the entire sheet surface by upwardly raising the first regions and downwardly recessing the second regions.
JP 2009-286249A discloses a floor panel provided with a protrusion. In the protrusion, triangular flat surfaces are combined to have an angle. A flat surface is formed around the protrusion.
JP 2006-297966A discloses a floor structure of a vehicle body. This floor structure includes a floor panel. The floor panel is provided with beads. The beads have a concentric arc shape whose center is a portion where a side sill and a cross-member intersect each other.